The invention relates to a disc brake for a commercial vehicle having a caliper that straddles a brake disc and is fastened in an axially displaceable manner in relation to the brake disc by two connecting bearings to a brake carrier arranged on the vehicle side. The connecting bearings each have a guide bar, which is rigidly connected to the brake carrier and is guided in a slide bearing of the caliper for axial displacement thereof.
In disc brakes of the concerned type, which are known by the term sliding-caliper disc brakes, the caliper is connected to the brake carrier on the vehicle side by connecting bearings. In this case guide bars, which are a component of the connecting bearings and are usually connected to the brake carrier by a threaded fastener, are guided in slide bearings of the caliper such that axial displacement of the caliper with respect to the positionally fixed brake carrier is possible.
One of the slide bearings is in the form of a fixed bearing with a small amount of sliding play, while the other functions as a movable bearing by which, in particular, manufacturing tolerances are compensated.
In addition to the guide bars, the connecting bearings include radially elastic damping bushings that are intended to prevent the caliper, which under operating conditions is movable radially to a certain extent, from striking against the guide bar and producing disturbing clattering noises, above all in vehicles used for conveying passengers. Further, the damping bushings are used for sliding mounting of the guide bar, primarily in the movable bearing, where they are held in the brake caliper, or in a bearing bush fastened therein. A design of this type is known from the category-defining DE 102 45 027 A1.
The damping bushing shown in DE 102 45 027 A1 has on its inner circumferential surface ribs of uniform cross section. The ribs each delimit adjacent grooves. The slideability of the guide pin and the radial damping properties are influenced by these ribs. However, these known damping bushings are not suitable for dealing adequately with the various demands in mobile operation, in particular with regard to shocks that arise.
In particular in the case of a fixed bearing, if the damping bushings, in combination with the bearing bush, jointly form the slide bearing for the guide bar, in which slide bearing both the damping bushing and, in axial prolongation, the bearing bush perform sliding functions, then clashing can occur under correspondingly heavy radial loading of the damping bushing or of the caliper as a whole with respect to the guide bar. The damping bushing, which, moreover, is preferably made of an elastomer, is compressed so far, on account of its damping characteristic curve, that the metal bearing bush contacts the guide bar. This causes the unpleasant clattering noises already mentioned, so that the known disc brake does not offer an optimum solution with regard to operating comfort.
It is the object of the invention to develop a disc brake of the above-mentioned type in such a manner that an improvement in operating comfort and enhanced service life are achieved with low cost and complexity in terms of design and manufacture.
This and other objects are achieved by a disc brake for a commercial vehicle having a caliper that straddles a brake disc and is fastened in an axially displaceable manner in relation to the brake disc by two connecting bearings to a brake carrier arranged on the vehicle side. The connecting bearings each have a guide bar, which is rigidly connected to the brake carrier and is guided in a slide bearing of the caliper for axial displacement thereof. At least one connecting bearing is provided with a radially elastic damping bushing which surrounds in zones the guide bar and has grooves delimited laterally by ribs. The damping bushing is configured to have a progressive damping behavior in a radial loading direction.
A disc brake according to the invention clamps the radial loads, which arise in mobile operation of the vehicle, in an absolutely reliable way, specifically to the extent that the clashing which has been mentioned—in principle the abolishing of the damping property by overcoming of the damping forces—is eliminated.
Especially if the damping bushing is arranged in the region of the fixed bearing while, as mentioned, both the damping bushing and the bearing bush perform sliding functions through contact with the guide bar, the bearing bush is effectively prevented from striking against the guide bar in the event of corresponding shocks while driving. Undesired noise generation resulting therefrom is prevented by the invention. Because the guide bar is thereby naturally subjected to lower mechanical loading, its service life, like that of the bearing bush, is increased.
But the invention offers advantages even if the damping bushing is used in the movable bearing, since the guidance property of the damping bushing is improved by the progressive damping behavior thereof in the radial loading direction. This is because, with increasing radial load, the damping bushing becomes stiffer in its elastic behavior, resulting in the advantage mentioned.
According to an advantageous development of the invention, it is provided that at least some of the ribs are thicker than the other ribs. Alternatively or additionally, some of the ribs may be wider, and their spacing from one another may vary, additionally or optionally.
The cross-sectional contour of the ribs may vary; the flanks thereof are preferably curved concavely and merge into a flat upper face which may be a contact face with the guide bar or the guide bush. It is also possible, however, to adapt the flat upper face to the contour of the guide bush or of the bearing bush. The concave shape of the flanks of the ribs results in a concave configuration of the groove contour, which has an arcuate or otherwise curved configuration.
The disposition of the ribs may be circumferential, axial or diagonal. It is also possible to provide the outer and inner circumferential surface of the damping bushing with ribs, in which case, the upper faces of at least some of the ribs form contact faces too with the guide bar or the bearing bush.
With a corresponding radial loading, the ribs, which are adapted thereto in their progressive behavior, may first be deformed to the extent that they form in that respect a continuous surface with the adjacent grooves. Only with further increasing load do the other ribs, designed for this purpose, come into use, so to speak. It can be understood that a very finely-tuned damping behavior of the damping bushing can be predetermined and therefore realized without difficulty.
A further major advantage of the invention is that the enhanced comfort of the disc brake can be achieved without additional cost, as compared to the damping bushings used hitherto, which is especially noteworthy if account is taken, in particular, of the series production of the component, which is manufactured in large volume.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.